Lubricating oil composition

ABSTRACT

The present invention provides a lubricating oil composition excellent in wear-resistant properties and frictional characteristics. The present invention relates to a lubricating oil composition containing a lubricating base oil 
     (A) a complex obtained by reacting a metallic salt of dithiophosphoric acid having lipophilic groups, the average number of the carbon atoms of which is 4 or more, with a primary alkylamine having 8 or less carbon atoms, and 
     (B) at least one kind of compound selected from the group consisting of oxymolybdenum sulfide dithiocarbamate, oxymolybdenum sulfide organophosphorodithioate, fatty esters, and organic amides.

FIELD OF THE INVENTION

The present invention relates to a lubricating oil composition, and morespecifically, one excellent in wear-resistant properties and frictionalcharacteristics. The lubricating oil composition of the presentinvention can be used as a lubricating oil for automotive internalcombustion engines (engine oil), and also in a wide range of fields asgear oils, automatic transmission fluids (ATF), power-steering oils (PSoil), spindle oils, hydraulic fluids, and industrial lubricating oils.

BACKGROUND OF THE INVENTION

Since zinc dithiophosphates (below called "Zn-DTP") such as zincdialkyldithiophosphates show an excellent wear-inhibiting performance,besides acting as an antioxidant and a corrosion inhibitor, they havebeen generally used as an additive for engine oils.

However, since phosphorus (P) contained in Zn-DTP poisons any automotiveexhaust emission purification catalyst and any automotive oxygen sensor,an engine oil to which Zn-DTP is added has had a problem in that theperformance of any exhaust-gas emission control system decreasessignificantly. Conventionally to resolve this problem a method ofdecreasing the added amount of Zn-DTP to lower the amount of phosphorusin the engine oil has been adopted. However, when the amount of Zn-DTPdecreases, problems are caused such that the wear-resistant propertiesof the lubricating oil decrease and in that the engine durabilitydecreases due to the wear of the valve-gear system. Thus whiledecreasing the added amount of Zn-DTP, other additives, such as anash-free detergent dispersant and a metal detergent have been used withZn-DTP to maintain performances necessary for an engine oil.

However, when both Zn-DTP and an ash-free detergent dispersant such as apolyalkenyl succinimide are used, a problem arises such that bothcompounds are the first to react in a base oil to result in the effectsof Zn-DTP being masked and its activity being impaired. Accordingly, toattain sufficient wear-resistant properties, Zn-DTP must be used in arelatively high amount, and thus it has been difficult to decrease thephosphorus content.

SUMMARY OF THE INVENTION

1. Disclosure of the Invention

The object of the present invention resides in providing a lubricatingoil composition excellent in wear-resistant properties and frictionalcharacteristics.

2. Means to Resolve the Problems

As a result of the extensive study by the inventors of the presentinvention to resolve the above problems, they found that besides thewear-resistant properties of a lubricating oil being improved, thecoefficient of friction of the oil significantly decreased by (1) addingto a lubricating base oil a complex of a metallic salt ofdithiophosphoric acid (below called "M-DTP") with a primary alkylaminehaving a short chain and (2) containing in a lubricating base oil atleast one kind of compound selected from the group consisting of anoxymolybdenum sulfide dithiocarbamate (below called "Mo-DTC"), anoxymolybdenum sulfide organophosphorodithioate (below called "Mo-DTP"),a fatty ester, and an organic amide compound.

Based on this finding they accomplished the present invention.

Thus according to the present invention a lubricating oil composition isprovided by containing in a lubricating base oil (A) a complex obtainedby reacting a metallic salt of dithiophosphoric acid having lipophilicgroups, the average number of the carbon atoms of which is 4 or more,with a primary alkylamine having 8 or less carbon atoms, and (B) atleast one kind of compound selected from the group consisting of anoxymolybdenum sulfide dithiocarbamate, an oxymolybdenum sulfideorganophosphorodithioate, a fatty ester, and an organic amide.

DETAILED DESCRIPTION OF EMBODIMENT

The present invention will be described in detail below.

(Lubricating Base Oil)

Lubricating base oils used in the present invention are not specificallylimited, and various kinds of conventionally-known mineral oils andsynthetic lubricating oils can be used. Exemplified as the mineral oilsare raffinates obtained by solvent-refining a lubricating oil materialwith an aromatic extraction solvent such as phenol or furfural, ahydrogenation-treated oil obtained by hydrogenation treatment with acatalyst for hydrogenation treatment such as cobalt or molybdenumsupported on silica-alumina as a carrier, and a mineral oil such as alubricating oil distillate obtained by the isomerization of wax, as, forexample, 60 Neutral Oil, 100 Neutral Oil, 150 Neutral Oil, 300 NeutralOil, 500 Neutral Oil, Bright Stock, etc. As the synthetic lubricatingoils, poly-α-olefins, polybutene, alkylbenzenes, polyol esters, anddibasic acid esters, are exemplified. Such a base oil can be used aloneor as a mixture of two or more kinds. When such a lubricating base oilis used in an engine oil, its kinetic viscosity is ordinarily 3 to 20cSt at 100° C.

(Metallic Salts of Dithiophosphoric Acid)

The metallic salts of dithiophosphoric acid (M-DTP) used in the presentinvention are compounds represented by following general formula (I):##STR1## wherein M is a metal atom selected from zinc, copper, nickel,iron, cadmium, silver, lead, antimony,/in, and bismuth, and each of R₁to R₄ is independently selected from lipophilic groups having 1 to 30carbon atoms provided that the average number of the carbon atoms of thefour lipophilic groups is 4 or more.

Each of these M-DTPs may be used alone, or two or more kinds of theM-DTPs may be used together.

As the lipophilic group, saturated and unsaturated alkyl groups,alkylaryl groups, and arylalkyl groups, are exemplified. The fourlipophilic groups can be varied from those in which four of thelipophilic groups are all the same to those in which each of them isdifferent. When the average number of the carbon atoms of the fourlipophilic groups of this M-DTP is less than 4, even if the M-DTP isused with a primary alkylamine, it is difficult to obtain a uniformlubricating oil composition, since the solubility of M-DTP in alubricating oil is poor. Since an organic metal-based wear-resistantagent generally fulfills its function by being adsorbed on the surfaceof metals, it is necessary to have an appropriate solubility in the oil.

In contrast, when an M-DTP is used in which the average number of thecarbon atoms of the four lipophilic groups exceeds 13, although thesolubility of the M-DTP in a lubricating oil is good, the wear-resistantproperties decrease. From the aspect of the functionality ofwear-resistant properties etc., the upper limit of the average number ispreferably 13.

From the aspect of the functionalities such as the ease of theirsynthesis and wear-resistant properties, usually M-DTPs in which fourlipophilic groups are alkyl groups having 4 or more carbon atoms areespecially preferred.

As the metal atoms (M), zinc, copper, nickel, iron, cadmium, silver,lead, antimony, tin, and bismuth, are exemplified. Among others, fromthe aspect of functionalities such as the ready availability andwear-resistant properties, zinc (Zn) is especially preferred.

(Primary Alkylamine)

As the primary alkylamines used in the present invention, relativelyshort-chain alkylamines such as n-propylamine, n-butylamine,n-pentylamine, n-hexylamine, n-heptylamine, and n-octylamine, areexemplified.

When preparing a complex with an alkylamine, the amount used of M-DTP isadjusted such that the compounding ratio in a lubricating oilcomposition based on the total amount of the composition becomes usually0.05 to 7% by weight, preferably 0.2 to 5% by weight, more preferably0.3 to 2% by weight. If the compounding ratio of the M-DTP is too low,the effect in imparting wear-resistant properties is insufficient, andif the ratio is too high the wear-resistant properties do not increaseabove a certain degree and corrosion of metals can be caused.

The compounding ratio of the primary alkylamine is 0.001 to 0.5% byweight, preferably 0.01 to 0.3% by weight. If the compounding ratio ofthe primary alkylamine compound is too low, the effect obtained by thecompound is insufficient, and if the ratio is too high thewear-resistant properties often decrease rather than increase.

It is preferable to first form a complex of M-DTP with a primaryalkylamine, and then to add the complex to a lubricating oil, since thepreferential reaction of M-DTP with an ash-free detergent dispersant isdepressed, and thus a lubricating oil composition having excellentwear-resistant properties can be obtained. To first form a complex ofM-DTP with a primary alkylamine, a preferable process is to add them toa lubricating base oil such that the concentration of the complex ishigh, and then to heat the obtained composition. For example, M-DTP isadded and mixed with a primary alkylamine in a given ratio, and, ifdesired, the obtained mixture is diluted with the base oil to an amountequaling several times the amount of the mixture, and the obtainedmixture is stirred, preferably at 40° to 120° C., more preferably at 60°to 100° C., preferably for 1 to 60 minutes, more preferably for 5 to 30minutes, to form a complex. The higher the heating temperature is, theshorter is the time required to form a complex which is uniformlysolubilized in a base oil. The resulting solution of the complex is usedas a lubricating oil composition as such, or it is further diluted witha lubricating oil and used as a uniform lubricating oil compositioncontaining M-DTP and a primary alkylamine in a desired ratio.

(Additives Used Together)

In the present invention, to a lubricating base oil, together with acomplex of a metallic salt of dithiophosphoric acid and a oxymolybdenumsulfide organophosphorodithioates, fatty esters, and primary alkylamine,is added at least one kind of compound selected from the groupconsisting of oxymolybdenum sulfide dithiocarbamates, organic amidecompounds.

Mo-DTC and Mo-DTP

The oxymolybdenum sulfide dithiocarbamates (Mo-DTC) and oxymolybdenmsulfide organophosphorodithioates (Mo-DTP) are organic molybdenumcompounds represented by following general formulas (II) and (III)respectively: ##STR2## in which formulas (II) and (III) R₅ to R₈, whichmay be the same or different, are each a hydrogen atom, an alkyl grouphaving 1 to 20 carbon atoms, a cycloalkyl group having 6 to 26 carbonatoms, an aryl, alkylaryl, or arylalkyl group having 6 to 26 carbonatoms, or a hydrocarbon group containing an ester bond, ether bond,alcohol group, or carboxyl group. X₁ and X₂, which may be the same ordifferent, are each an oxygen atom or a sulfur atom. Y₁ and Y₂, whichmay be the same or different, are each an oxygen atom or a sulfur atom.

In general formulas (II) and (III) R₅ to R₈ are each preferably asaturated or unsaturated alkyl group having 6 to 18 carbon atoms, acycloalkyl group having 12 to 24 carbon atoms, or an alkylaryl grouphaving 12 to 24 carbon atoms. As the preferred examples of thesesubstituents are alkyl groups or unsaturated alkyl groups (alkenylgroups) having 6 to 18 carbon atoms such as n-hexyl, 2-ethylhexyl,n-octyl, nonyl, decyl, lauryl, tridecyl, oleyl, and linoleyl, andalkylaryl groups substituted by an alkyl group having 3 to 18 carbonatoms, such as nonylphenyl.

Not only when Mo-DTC or Mo-DTP is used alone, but also when they areused together, is the compounding ratio of Mo-DTC and/or Mo-DTP based onthe total composition of 0.01 to 10% by weight, preferably 0.05 to 5% byweight, more preferably 0.1 to 1% by weight. If the compounding ratio isless than 0.01% by weight, the wear-decreasing effect of the compositionis low, and if it is too high, a problem such as the occurence ofcopper-corrosive properties tends to appear. To aim to lower thephosphorus content in a lubricating oil, as the organic molybdenumcompound, it is preferred to use Mo-DTC alone, or when Mo-DTP is used itis used such that its compounding ratio is as low as 0.2% by weight orless. By using a combination of specified additives, even if the ratioused of the organic molybdenum compound is relatively low, an excellenteffect in regards to the coefficient of friction can be obtained.

Fatty Ester

As the fatty esters used in the present invention, monoesters anddiesters of a fatty acid and glycerine or sorbitan are exemplified.

The fatty glyceride is a monoester represented by following generalformula (IV) or a diester represented by following general formula (V):##STR3## in which formulas (IV) and (V) R₉ to R₁₁ are each a saturatedor unsaturated alkyl group having 8 to 22 carbon atoms.

The fatty ester may be used alone or as a mixture of two or more kindsof the esters. Based on the total composition its compounding ratio is0.01 to 10% by weight, preferably 0.05 to 5% by weight. If thecompounding ratio is too low any improved effect in the frictionalcharacteristics is too low, and if it is too high the wear-resistantproperties worsen.

Organic Amide Compound

An organic amide compound used in the present invention is a compoundrepresented by following general formula (VI): ##STR4## in which formula(VI) R₁₂ and R₁₃, which may be the same or different, are each ahydrogen atom, an alkyl group having 1 to 20 carbon atoms, a cycloalkylgroup having 6 to 26 carbon atoms, or an aryl, alkylaryl, or arylalkylgroup having 6 to 26 carbon atoms, an alkylene oxide group having 2 to30 carbon atoms, and R₁₄ is a hydrogen atom, an alkyl group having 1 to20 carbon atoms, an cycloalkyl group having 6 to 26 carbon atoms, anaryl, alkylaryl, or arylalkyl group having 6 to 26 carbon atoms, or ahydrocarbon group having an ester bond, an ether bond, or a carboxylgroup.

The alkylene oxide group used here is a group represented by followinggeneral formula (VII) or (VIII): ##STR5## in which formulas (VII) and(VIII) R' is a hydrogen atom or a methyl group, and n is an integer of 1to 10.

In general formula (VI) R₁₂ and R₁₃ are preferably each a hydrogen atom,an alkyl group having 2 to 8 carbon atoms, a cycloalkyl group having 8to 14 carbon atoms, an alkylaryl group having 8 to 14 carbon atoms, oran alkylene oxide in which n is 1 to 5, and R₁₄ is preferably asaturated or unsaturated alkyl group having 6 to 18 carbon atoms, acycloalkyl group having 12 to 24 carbon atoms, or an alkylaryl grouphaving 12 to 24 carbon atoms.

As such organic amides, oleic amide and lauric amide are exemplified.

The compounding ratio of the organic amide compound is 0.01 to 10% byweight, preferably 0.01 to 5% by weight, more preferably 0.05 to 2% byweight. By adding the organic amide compound, while copper-corrosiveproperties are lowered, the coefficient of friction can be decreasedfrom the beginning. If the compounding ratio is too small, the effect indecreasing friction is low, and if too high the effect does not increaseabove a certain degree.

(Lubricating Oil Composition)

The lubricating oil composition of the present invention can be preparedby adding said various ingredients to a lubricating base oil. M-DTP anda primary alkyl amine are first reacted to form a complex, and then thecomplex is added to the lubricating oil.

To a lubricating oil composition of the present invention, if required,a wear-resistant agent, a friction-decreasing agent, an ash-freedetergent dispersant, an anti-oxidant, a metal detergent, a viscosityindex-improving agent, a pour-point lowering agent, a rust-preventiveagent, a defoaming agent, a corrosion-preventive agent, etc., may besuitably added.

As wear-resistant agents, zinc salt of dithiocarbamic acid, phosphoricesters, and amine salts of phosphoric esters, are exemplified.

As ash-free detergent dispersants, polyalkenyl succinic imides,polyalkenyl succinic amides, alkylbenzyl amines, boron derivatives ofpolyalkenyl succinic imides, and boron derivatives of alkylbenzylamines, are exemplified.

As the anti-oxidant agents, amine-based anti-oxidant agents such asalkylated diphenylamines, phenyl-α-naphtylamine, and alkylatedα-naphtylamine, and phenol-based anti-oxidant agents such as2,6-di-t-butylphenol and 4,4'-methylene-bis-(2,6-di-t-butylphenol), areexemplified. The agent is usually used in a ratio of 0.05 to 2% byweight.

Exemplified as the metal detergents are Ca-sulfonate, Mg-sulfonate,Ba-sulfonate, Ca-phenate, Ba-phenate, Mg-phenate, Ca-salicylate,Mg-salicylate, and Ba-salicylate. They are usually used in a ratio of0.1-5% by weight.

Exemplified as the viscosity-index improving agents arepolymethylmethacrylate-type, polyisobutyrene-type,ethylene-propylene-copolymer-type, and hydrogenated styrene-butadienecopolymer-type agents. They are usually used in a ratio of 1-35% byweight.

Exemplified as the rust-preventive agents are alkenyl succinic acids andpartially esterified alkenyl succinic acids.

As the defoaming agents, dimethyl polysiloxane and polyacrylate areexemplified.

By adopting the above constitution the lubricating oil compositions ofthe present invention can significantly decrease the coefficient offriction, besides showing superior wear-resistant properties. Also, byusing zinc dithiocarbamate (Zn-DTC) with M-DTP, the ratio of M-DTP canbe significantly decreased, to obtain a lubricating oil composition witha lower content of phosphorus than those conventionally used.

Because of the use of a combined system of M-DTP and a primaryalkylamine, the lubricating oil compositions of the present inventionhave properties, such as oxidation stability and anti-coking properties,besides wear-resistant and extreme-pressure properties.

Although the reason why the lubricating oil compositions of the presentinvention show excellent wear-resistant properties is unclear, it isconsidered that due to the formation of a complex of M-DTP and a primaryalkylamine, the reaction of M-DTP with an ash-free detergent dispersantis depressed, thus making the adsorption of M-DTP on the surface ofmetals easy.

The lubricating oil compositions are used for automotive engine oils,gear oils, automatic transmission fluids, power-steering oils, spindleoils, hydraulic fluids, and industrial lubricating oils.

The present invention is especially illustrated by the followingExamples and Comparative Examples, but it is not limited to thoseExamples.

EXAMPLES 1 TO 8, AND COMPARATIVE EXAMPLES 1 TO 4

Lubricating oil compositions were prepared by adding the variousingredients listed in Table 1. In the Table the ratios of the variousingredients are represented by % by weight. The remaining portion is theratio of a lubricating base oil. Zn-DTP, in which the number of carbonatoms of a lipophilic group is 6, is first reacted with n-hexylamine toform a complex, and then the complex is used.

Various ingredients are shown below.

(1) Lubricating base oil

150 Neutral mineral oil (The kinetic viscosity at 100° C. is 5.1 cSt.)

(2) Zn-DTP

A commercially available Zn-DTP: a Zn-DTP having four s-hexyl groups.

After the Zn-DTP is reacted with n-hexylamine in a mineral oil to form acomplex, the complex was further diluted with a mineral oil.

(3) Mo-DTC ##STR6## wherein 2EH is a 2-ethylhexyl group. (4) Mo-DTP##STR7## wherein 2EH is a 2-ethylhexyl group. (5) Fatty glyceride##STR8## wherein R is an oleyl group. (6) Organic amide compound

Oleic amide

Treatment for Forming a Complex

Zn-DPT in which the number of carbon atoms of a lipophilic group is 6,n-hexylamine, and a mineral oil, were mixed in a weight ratio of1:0.28:1 in a reactor equipped with a stirrer, and the obtained mixturewas heated at 60° C. for 5 minutes with stirring. The resulting solutioncontaining the formed complex was further diluted with a mineral oil tobe prepared such that the content of Zn-DTP was 0.5% by weight or 1.0%by weight.

For the obtained lubricating oil compositions, the wear-resistantproperties and coefficients of friction were evaluated. The results arelisted in Table 1. The method of measuring was as shown below.

Method of Measuring Frictional Characteristics and Wear-resistantProperties

By using the Shell four-ball-type test, the coefficients of friction andball diameters after wear (mm) were measured. The conditions were asfollows:

Load: 40 kg

Oil temperature: 90° C.

Number of revolutions: 1,800 rpm

Test time: 30 minutes

                                      TABLE 1                                     __________________________________________________________________________               Examples                Comparative Examples                                  1  2  3  4  5  6  7  8  1  2  3  4                                 __________________________________________________________________________    Commercially Available                                                                   0.5                                                                              1.0                                                                              0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              0.5                                                                              1.0                                                                              0.5                                                                              1.0                               Zn--DTP(s-C.sub.6)                                                            n-hexylamine                                                                             0.14                                                                             0.28                                                                             0.14                                                                             0.14                                                                             0.14                                                                             0.14                                                                             0.14                                                                             0.14                                                                             0.14                                                                             0.28                                                                             -- --                                Mo--DTC    0.15                                                                             0.15                                                                             1.5                                                                              0.15                                                                             0.5                                                                              -- 0.15                                                                             0.15                                                                             -- -- -- --                                Mo--DTP    -- -- -- -- -- 0.15                                                                             -- 0.075                                                                            -- -- -- --                                Fatty Glyceride                                                                          0.075                                                                            0.075                                                                            0.075                                                                            1.5                                                                              -- 0.075                                                                            0.075                                                                            -- -- -- -- --                                Oleic Amide                                                                              -- -- -- -- 0.3                                                                              -- 0.3                                                                              0.3                                                                              -- -- -- --                                Coefficient                                                                              0.053                                                                            0.056                                                                            0.052                                                                            0.053                                                                            0.052                                                                            0.057                                                                            0.051                                                                            0.053                                                                            0.083                                                                            0.090                                                                            0.120                                                                            0.125                             of Friction                                                                   Ball Diameter                                                                            0.43                                                                             0.41                                                                             0.43                                                                             0.45                                                                             0.44                                                                             0.45                                                                             0.44                                                                             0.45                                                                             0.042                                                                            0.39                                                                             0.49                                                                             0.43                              After Wear (mm)                                                               __________________________________________________________________________

As is clear from the results as listed in Table 1, any lubricating oilcomposition of the present invention shows, besides a significantly lowcoefficient of friction and good low-friction properties, that the balldiameter after wear is small and that the wear-resistant properties aregood. In contrast, when only the combination system of Zn-DTP andn-hexylamine is used (Comparative Examples 1 and 2), the effect indecreasing the coefficient of friction was insufficient. Whenn-hexylamine was not used (Comparative Examples 3 and 4) the coefficientof friction was further increased, and the frictional characteristicswere insufficient.

According to the present invention, lubricating oil compositionsexcellent in wear-resistant properties and frictional characteristicsare provided. Although any lubricating oil composition of the presentinvention has a low phosphorus content, it shows excellentwear-resistant properties and a low coefficient of friction, and thus itis especially suitable for internal combustion engines.

We claim:
 1. A lubricating oil composition comprising a major portion ofa lubricating base oil and as additives:(A) a complex obtained byreacting (1) a metallic salt of dithiophosphoric acid having lipophilicgroups, the average number of carbon atoms in each of the lipophilicgroups is between 4 and 13 carbon atoms with (2) a primary alkylaminehaving 8 or less carbon atoms, and (B) at least one compound selectedfrom the group consisting of oxymolybdenum sulfide dithiocarbamate,oxymolybdenum organophosphorodithioate, fatty esters, and organicamides, with the additives being present in a minor amount to providewear resistant properties and a decreased coefficient of friction to thecomposition.
 2. A lubricating oil composition according to claim 1wherein said complex is present in said composition in an amount toprovide from about 0.2 to about 5% by weight of said metallic salt ofdithiophosphoric acid and from about 0.01 to about 0.3% by weight ofsaid primary alkylamine, and the at least one compound component (B) ispresent in said composition in an amount of from about 0.01 to about 5%by weight.
 3. A lubricating oil composition according to claim 2 whereinsaid metallic salt of dithiophosphoric acid is a zinc salt and saidprimary alkylamine is N-hexylamine.
 4. A lubricating oil compositionaccording to claim 3 wherein said metallic acid of dithiophosphoric acidis zinc O,O-dihexyl dithiophosphate.
 5. A lubricating oil compositionaccording to claim 4 wherein the at least one compound of component (B)comprises an oxymolybdenum sulfide dithiocarbamate.
 6. A lubricating oilcomposition according to claim 4 wherein the at least one compound ofcomponent (B) comprises an oxymolybdenum organophosphorodithioate.
 7. Alubricating oil composition according to claim 5 wherein the at leastone compound of component (B) additionally comprises an oxymolybdenumorganophosphorodithioate.
 8. A lubricating oil composition according toclaim 5 wherein the at least one compound of component (B) additionallycomprises a fatty glyceride that comprises 50% by weight of an oleylmonoester of glycerine and 50% by weight of an oleyl diester ofglycerine.
 9. A lubricating oil composition according to claim 6 whereinthe at least one compound of component (B) additionally comprises afatty glyceride that comprises 50% by weight of an oleyl monoester ofglycerine and 50% by weight of an oleyl diester of glycerine.
 10. Alubricating oil composition according to claim 5 wherein the at leastone compound of component (B) additionally comprises oleic amide.
 11. Alubricating oil composition according to claim 7 wherein the at leastone compound of component (B) additionally comprises oleic amide.
 12. Alubricating oil composition according to claim 8 wherein the at leastone compound of component (B) additionally comprises oleic amide.